This invention relates generally to antenna elements and more particularly to phased array antenna elements of such type which are adapted selectively to radiate radio frequency energy of either circular or linear polarization.
As is known in the art, a collimated beam of radio frequency energy may be formed and steered by controlling the phase of the energy radiated from each one of a plurality of antenna elements in an array thereof. It is also known that in some applications, as where the effect of rain echos is to be reduced, it is desirable that the polarization of such radiated energy be circular. One such antenna element adapted for such application is described in U.S. Pat. No. 3,736,535 issued May 29, 1973, inventors Mohr et al, and assigned to the same assignee as the present invention. In other applications it is desirable that the polarization of the radiated energy be horizontal (as for terrain avoidance or terrain mapping applications) and, in still other applications, that polarization of such energy be vertical (as for acquisition, search or collision avoidance applications).
In view of the foregoing it is highly desirable that an antenna array be adapted selectively to radiate either circularly polarized radiation or linearly polarized radiation. Further, in order to simplify the beam steering electronics, it is further desirable that each antenna element in an array be a reciprocal device. With antenna elements of such nature, the same beam steering control signals may be applied during any reception period as were applied during a corresponding transmission period to direct transmitted energy in any desired direction.